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    Subject[PATCH 14/16] nbd: Set SOCK_MEMALLOC for access to PFMEMALLOC reserves
    Date
    Set SOCK_MEMALLOC on the NBD socket to allow access to PFMEMALLOC
    reserves so pages backed by NBD, particularly if swap related, can
    be cleaned to prevent the machine being deadlocked. It is still
    possible that the PFMEMALLOC reserves get depleted resulting in
    deadlock but this can be resolved by the administrator by increasing
    min_free_kbytes.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    ---
    drivers/block/nbd.c | 6 +++++-
    1 file changed, 5 insertions(+), 1 deletion(-)

    diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
    index 061427a75d..76bc96f 100644
    --- a/drivers/block/nbd.c
    +++ b/drivers/block/nbd.c
    @@ -154,6 +154,7 @@ static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
    struct msghdr msg;
    struct kvec iov;
    sigset_t blocked, oldset;
    + unsigned long pflags = current->flags;

    if (unlikely(!sock)) {
    dev_err(disk_to_dev(nbd->disk),
    @@ -167,8 +168,9 @@ static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
    siginitsetinv(&blocked, sigmask(SIGKILL));
    sigprocmask(SIG_SETMASK, &blocked, &oldset);

    + current->flags |= PF_MEMALLOC;
    do {
    - sock->sk->sk_allocation = GFP_NOIO;
    + sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
    iov.iov_base = buf;
    iov.iov_len = size;
    msg.msg_name = NULL;
    @@ -214,6 +216,7 @@ static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
    } while (size > 0);

    sigprocmask(SIG_SETMASK, &oldset, NULL);
    + tsk_restore_flags(current, pflags, PF_MEMALLOC);

    return result;
    }
    @@ -405,6 +408,7 @@ static int nbd_do_it(struct nbd_device *nbd)

    BUG_ON(nbd->magic != NBD_MAGIC);

    + sk_set_memalloc(nbd->sock->sk);
    nbd->pid = task_pid_nr(current);
    ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
    if (ret) {
    --
    1.7.9.2


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